JPH0754146B2 - Hydraulic drive circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention drives at least two hydraulic pumps by one engine to perform different operations for each hydraulic pump, for example, a drive circuit for a wheel loader. As described above, the present invention relates to a hydraulic drive circuit suitable for a drive circuit of a construction machine that performs work by a combined operation of traveling and a front attachment.

[Conventional technology]

Most construction machines use hydraulic pressure because they can easily obtain a large operating force from a small power source and can drive a plurality of things from a single power source.

Among them, for example, in a wheel loader, a hydraulic pump for driving a wheel and a hydraulic pump for driving a bucket are separately provided, and a driving force can be given by one engine. An example of a hydraulic drive circuit used for such a wheel loader is shown in FIG.
This hydraulic drive circuit will be described with reference to FIG.

In the figure, this hydraulic drive circuit is used for one engine 1
A variable displacement hydraulic pump 2 for traveling drive driven by the engine 1 and a hydraulic pump 3 for bucket work; a hydraulic motor 4 rotatably driven by pressure oil from the variable displacement hydraulic pump 2; An actuator 7 for operating a displacement volume changing mechanism (hereinafter referred to as a swash plate) 6 of the displacement hydraulic pump 2, a direction switching valve 8 for switching the operating direction of the actuator 7, a tilt amount of the swash plate 6, and the engine 1
It is mainly composed of an accelerator lever 17 for simultaneously controlling the rotation speed of the.

The variable displacement hydraulic pump 2 is a double displacement type variable displacement pump, which is connected to a hydraulic motor 4 via main lines 10 and 11, and a mechanical transmission having a plurality of stages from an output shaft of the hydraulic motor 4. The driving force is transmitted to 12 and the differential gear 13,
Further, the differential gear 13 is transmitted to the wheel 5 to rotate the wheel 5. An auxiliary device 14 including a crossover release valve, a flushing valve, a charge pump, etc. is provided between the two main pipe lines 10 and 11, and constitutes a closed circuit together with the variable displacement hydraulic pump 2 and the hydraulic motor 4.

The variable displacement hydraulic pump 2 is controlled in its discharge direction and discharge flow rate by a swash plate 6, and this swash plate 6 is supplied from a hydraulic pressure source 15 via a pressure reducing valve 16 as a pressure control valve and a direction switching valve 8. It is operated by an actuator 7 which takes a position corresponding to the pressure of the hydraulic oil to be generated. Also, the actuator 7
Sets the tilt amount of the swash plate 6 by the pressure of the hydraulic oil supplied from the hydraulic pressure source 15 through the pressure reducing valve 16 and the pressure oil supply means such as the direction switching valve 8 and switches the direction switching valve 8 not shown. It is operated by the means to control the switching direction of the swash plate 6.

The pressure of the hydraulic oil supplied to the direction switching valve 8 is determined by the set pressure of the pressure reducing valve 16, and this set pressure is set according to the operation amount of the accelerator lever 17 that commands the target rotation speed of the engine 1. .

Now, when the directional control valve 8 is switched to the left side in FIG. 5, when the accelerator lever 17 is tilted in the direction of arrow A, the pressure reducing valve 16 operates via the spring 17a, and the pressure on the secondary side of the pressure reducing valve 16 is activated. To raise. The pressure oil on the secondary side of the pressure reducing valve 16 is supplied to the side chamber on the left side in the figure of the actuator 7 via the direction switching valve 8, and the side chamber on the right side of the actuator 7 is opened to the hydraulic tank 18 via the direction switching valve 8. Therefore, the swash plate 6 is tilted and the variable displacement hydraulic pump 2 sucks the pressure oil on the main pipe line 10 side and discharges it to the main pipe line 11 side to discharge the hydraulic motor 4.
Is rotated in the direction of arrow B. As a result, the wheel 5 is rotationally driven from the output shaft via the transmission 12 and the differential gear 13. At the same time, the hydraulic pump 3 is also driven by the engine 1 and pressure oil is sent to a work device (not shown) to perform a predetermined work.

When the accelerator lever 17 is further tilted in the direction of arrow A from the above state, the secondary side pressure of the pressure reducing valve 7 becomes higher and the swash plate 6
The variable displacement hydraulic pump 2
Discharge amount increases. As a result, the rotational speed of the hydraulic motor 4 is further increased, the rotational speed of the engine 1 is increased, the discharge amount of the hydraulic pump 3 is increased, and the output of the work device is increased.

From this state, when the accelerator lever 17 is returned in the opposite direction to the arrow C direction, the secondary pressure of the pressure reducing valve 16 decreases and the swash plate 6 is returned to the neutral direction by the spring force in the actuator 7. Be done. In response to this, the discharge amount of the variable displacement hydraulic pump 2 decreases, the rotation speed of the hydraulic motor 4 also decreases, and the wheel 5
Slows down. At the same time, the engine speed also drops,
The discharge amount of the hydraulic pump 3 also decreases.

When the direction switching valve 8 is switched to the right side opposite to the above, the swash plate 6 is tilted to the opposite side by the operation of the accelerator lever 17. As a result, the variable displacement hydraulic pump 2 is connected to the main pipeline 10
Then, the hydraulic motor 4 rotates in the direction opposite to the arrow B to rotate the wheel 5 in the reverse direction. In this case also, the variable displacement hydraulic pump 2 and the hydraulic motor 4 are controlled via the accelerator lever 17.

[Problems to be solved by the invention]

By the way, in the above hydraulic drive circuit, for example, when the transmission 12 is a high speed (H), constant speed (L) two-stage gearbox, the speed of a vehicle equipped with this hydraulic drive circuit and the accelerator lever 17 are changed. The relationship between the operation amount, that is, the stroke amount is as shown in FIG. According to the figure, stroke amount
Up to X _1, the vehicle speed increases in a quadratic curve due to an increase in the tilt amount of the swash plate 6 and an increase in the rotation speed of the engine 1. X ₁
When the stroke amount becomes larger than X ₁ after the swash plate 6 reaches the maximum tilt, the tilt amount of the swash plate 6 maintains the maximum value and the vehicle speed is
It is a function of only the engine speed of the engine 1, and increases in proportion to the engine speed. The absolute value of the vehicle speed is as indicated by reference sign H or L in the figure depending on the gear ratio of the gear box.

On the other hand, in the case of the construction machine having the above-described configuration, in order to increase the working speed of the working device driven by the hydraulic pump 3 at the time of working, the engine 1 is often used by increasing the rotation speed. In this case, depending on the content of the work, the traveling speed may increase even when the transmission 12 is switched to the low speed L side, which makes it difficult to perform a combined operation of the traveling operation and the working operation.

If a gear ratio that lowers the maximum speed in the low speed gear is selected as a countermeasure against this, the speed is insufficient when traveling alone, and it is necessary to frequently switch between the high speed H side gear and the constant speed L side gear. Further, if the reduction ratio of the gear reducer is increased and the vehicle speed is reduced in this way, the torque increases, and it is necessary to secure the strength of the axle in order to cope with the increase in the torque. However, securing such strength leads to cost increase and is not an appropriate measure.

As another measure, a variable throttle valve, also called an inching valve, is provided in the main conduit from the direction switching valve 8 to the actuator 7, and the variable throttle valve is operated via an operating means such as a pedal to reduce the pressure reducing valve 16 There is a method of limiting the discharge amount of the variable displacement hydraulic pump 2 by releasing a part of the pressure oil supplied to the actuator 7 through the direction switching valve 8. This method has a problem that the driver needs to operate a pedal or the like every time the work is performed, which imposes a heavy burden on the driver.

The present invention has been made in view of the above technical background, and an object thereof is to provide a hydraulic drive circuit in which a driver does not need to adjust the operating speed for each work in order to suppress the operating speed of a load. Is to propose. The other purpose is not to increase the torque even at low speed operation, therefore, sufficient strength is guaranteed even with a small-diameter axle, which has the same low cost as the conventional one,
It is to propose a hydraulic drive circuit that functions safely.

[Means for solving problems]

In order to solve the problems of the prior art and achieve the above object, the present invention is directed to one engine, a first hydraulic pump that drives a wheel, and a first hydraulic pump that drives a wheel, and is connected to the engine. A second hydraulic pump that drives the means, a hydraulic motor that is connected to the first hydraulic pump, and a hydraulic actuator that operates the discharge amount variable mechanism,
An accelerator lever that is connected to the engine and is capable of setting a target rotation speed of the engine by an operator, a hydraulic source that supplies pressure oil to the hydraulic actuator, and is connected between the hydraulic actuator and the hydraulic source, A hydraulic oil transmission means for increasing and transmitting the pressure of the pressure fluid supplied to the actuator according to an increase in the operation amount of the accelerator lever, and a hydraulic fluid transmission means connected to the actuator and the hydraulic fluid transmission means and supplied from the hydraulic pressure source. In the hydraulic drive circuit having a low pressure circuit for passing the hydraulic oil, the hydraulic oil from the hydraulic oil transmitting means is operated at a pressure value lower than the maximum pressure value at which the hydraulic oil transmitting means can output to the hydraulic actuator. Maximum pressure limiting means for limiting the maximum value of the supply pressure to the hydraulic actuator by bypassing the low pressure circuit And an actuating means operated by the operator to selectively actuate the maximum pressure limiting means, and when the actuating means selects the actuation of the maximum pressure limiting means, the engine speed is increased by operating the accelerator lever. Based on the above, when the rotation speeds of the first and second hydraulic pumps increase, the discharge flow rate of the second hydraulic pump increases in accordance with the increase of the engine rotation speed.
The hydraulic pump is configured to be controlled to a discharge flow rate that is limited to a maximum value that is originally output according to the value set by the maximum pressure limiting means.

In order to limit the pressure by the maximum pressure limiting means, at least one of the actual operating speed and the target speed of the engine is detected by the detecting means, and the detected pressure detected by the detecting means is set as the limit pressure as the paranator. It can also be configured as follows.

[Action]

According to the above means, when the operation of the maximum pressure limiting means is selected by the operating means, when the rotation speeds of the first and second hydraulic pumps are increased based on the increase of the engine rotation speed by the operation of the accelerator lever, 2 The discharge flow rate of the hydraulic pump increases as the engine speed increases, but the first hydraulic pump has a discharge flow rate that is limited from the maximum value originally output according to the value set by the maximum pressure limiting means. Since it is controlled to, after reaching the set value,
The pressure of the pressure oil supplied to the actuator can be made constant, and an output that changes only depending on the engine speed can be obtained.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

1 and 2 are for explaining a hydraulic drive circuit according to a first embodiment of the present invention. FIG. 1 is a circuit diagram of the hydraulic drive circuit, and FIG. 2 is a vehicle speed and an accelerator lever. It is a characteristic view which shows the relationship with a stroke amount. Hereinafter, constituent elements that are the same as or can be regarded as the same as those of the conventional example shown in FIG. 5 are denoted by the same reference numerals, and the description of the overlapping parts will be omitted as appropriate.

In FIG. 1, a pipe line 20 for supplying pressure oil to the direction switching valve 8
A sequence valve 22 is provided in parallel with the directional switching valve 8 in a bypass line 25 connecting the discharge line 21 with the pressure reducing valve.
An opening / closing valve 24 is provided in the pilot line 23 of the sequence valve 22 from the conduit 20 on the downstream side of 16. In addition, the sequence valve 22 can set the cracking pressure by the spring 22a. All others are third
The configuration is the same as the conventional example shown in the figure.

Next, the operation of the hydraulic drive circuit according to this embodiment configured as described above will be described.

In FIG. 1, the direction switching valve 8 is switched to either the left or right position, and the accelerator lever 17 is tilted in the direction of arrow A. At this time, the open / close valve 24 is assumed to be in the closed position. In this case, since the pilot line 23 of the sequence valve 22 is shut off by the opening / closing valve 24, the sequence valve 22 closes the illustrated position, that is, the bypass line 25. Therefore, the relationship between the stroke of the accelerator lever 17 and the vehicle speed is the same as the conventional one as shown by H or L in FIG.

Here, when the on-off valve 24 is switched to the opening direction when working in the low speed L range, the pilot line of the sequence valve 22 is changed.
23 is connected and the differential pressure across the pilot spool is spring 22
When the preset cracking pressure is reached by a, pipe 2
Connect 0 and 21. The spring that sets this cracking pressure
22a constitutes a means for detecting the pressure related to the target engine speed of the engine 1 and setting the set value for switching, that is, the maximum pressure to be limited. Then, if this switching set value is set to a value lower than the stroke amount X ₁ of the accelerator lever 17 at which the secondary increase in vehicle speed ends, for example, X ₂ , if the stroke amount is lower than X _2, The discharge amount of the variable displacement hydraulic pump 2 and the engine speed increase according to the amount, and the vehicle speed increases according to a quadratic curve on the low speed L side similar to the conventional one. When the stroke amount reaches X ₂ , the sequence valve 22 is activated to connect the pipe lines 20 and 21 to the bypass line 25.
To communicate with each other. As a result, the pressure of the hydraulic oil supplied to the actuator 7 via the direction switching valve 8 becomes constant, and the discharge amount of the variable displacement hydraulic pump 2 also becomes constant. Therefore, even if the stroke amount is larger than X ₂ , the discharge amount of the variable displacement hydraulic pump 2 remains a small value corresponding to the stroke amount X ₂ , so the vehicle speed is proportional to only the rotation speed of the engine 1. The speed, which is indicated by LL. All other operations are the same as in the conventional example.

As a result, the output of the engine 1 can be increased to the maximum limit and the work device can be driven by the maximum output of the second hydraulic pump 3 while keeping the vehicle speed lower than the conventional one.

As described above, according to the above-described embodiment, the sequence valve 22 is provided, and when the pressure becomes higher than the preset pressure, the operating pressure supplied to the actuator can be limited, so that the variable capacity It becomes possible to suppress the discharge amount of the hydraulic pump 1, and thereby it is possible to increase the number of gear stages without changing the mechanical transmission device. Further, once the optimum vehicle speed for work is set,
After that, the driver does not need to operate an inching pedal or the like that operates a variable throttle valve such as an inching valve, which simplifies the work.In addition, even if an extremely low vehicle speed is set, it does not affect the axle. The maximum value of the driving torque to be used is the same as that of the conventional one, and an excessive torque unlike when an extremely low speed is set by the gear reducer does not occur.Therefore, it is necessary to improve the strength of the axle against such an excessive torque. In addition, the relationship between the vehicle speed and the stroke amount of the accelerator lever 17 changes only by changing the setting value of the cracking pressure of the sequence valve 22. In addition, there are various effects such as the need to replace the gears of the gear reducer and the components associated therewith is eliminated.

In the above embodiment, the target engine speed is set to the accelerator lever.
Although the command is given by 17, the set pressure of the pressure reducing valve 16 is changed according to the operation amount of the accelerator lever 17 to control the hydraulic pressure supplied to the actuator 7, but one accelerator lever 17 is used. As a hydraulic drive circuit that can perform the same operation, a circuit that uses a differential pressure generated before and after the throttle according to the discharge amount of the fixed displacement pump is also considered. The essential part of this example is shown in FIG. 3 as a second embodiment.
In the figure, constituent elements which are the same as or can be regarded as the same as those of the embodiment shown in FIGS. 1 and 5 and the conventional example are designated by the same reference numerals.

In FIG. 3, a direction switching valve 8 for switching the operating direction is connected in parallel to an actuator 7 for operating the swash plate 6 of the variable displacement pump 2, and two ports of this direction switching valve are connected to the engine 1 by the engine 1. Fixed displacement pump driven
A high-pressure side pipeline 33 and a low-pressure side pipeline 34, which communicate with the upstream side and the downstream side of a throttle 32 provided in a discharge pipeline 31 from 30, are respectively connected. The engine 1 has an accelerator lever 17
The target rotational speed is commanded according to the operation amount of the fixed displacement pump 30, and the fixed displacement pump 30 discharges the pressure oil according to the rotation of the engine 1.
The fixed displacement pump 30 has a function of generating an operating pressure of the actuator 7 and a function of charging the pressure oil to the main pipes 10 and 11 of the closed circuit for driving the hydraulic motor 4.

Further, a bypass line 25 having a sequence valve 22 interposed is connected between a pipeline 33 corresponding to the pressure oil supply means side and a pipeline 34 corresponding to the low pressure circuit side, and an open / close valve is provided in a pilot line 23 of the sequence valve 25. 24 are provided. Other parts, which are not particularly described, are configured similarly to the conventional example and the first embodiment.

With the above-mentioned configuration, the same effect as that of the first embodiment can be obtained by utilizing the differential pressure generated before and after the diaphragm 32.

In the first and second embodiments described so far, the target rotational speed of the engine 1 is detected from the pressure on the downstream side of the pressure reducing valve 16 or the actual operating rotational speed is detected from the pressure difference generated before and after the throttle 32, and the sequence is performed. By switching the valve by setting the cracking pressure of the valve 22, the pressure oil is derived from the high pressure side pipe lines 20, 33 corresponding to the pressure oil supply means side to the low pressure side pipe lines 21, 34 corresponding to the low pressure circuit. The detection means and the valve control means (actuating means) are constituted by mechanical means.

On the other hand, the detection means and the valve control means (operating means)
It is conceivable to configure the by an electric means. This example is shown in FIG. 4 as a third embodiment. In the figure, the same reference numerals are given to the same or the same components as those of the above-mentioned embodiment and the conventional example.

In FIG. 4, the engine 1 is provided with a tachometer 40 for detecting the number of revolutions, and the tachometer 40 electrically processes the number of revolutions detected by the tachometer 40 to detect the detected number of revolutions. A processing device 43 is connected to the switch device 42, which can arbitrarily select an opening / closing switching set value of the electromagnetically operated opening / closing valve 41 described below using the number as a parameter and output a switching signal of the opening / closing valve 41. In this case, the switching setting value setting means and the valve control means are constituted by the processing device 43 and the switch device 42. Further, the on-off valve 41 is a bypass line connecting both the pipe lines 33 and 34 as in the second embodiment.
The open position and the closed position are electromagnetically selected by the switching output of the switch device 42 which is inserted in 25 and which operates by the output from the processing device 43. Other than that, each part which is not particularly described has the same structure as that of the second embodiment shown in FIG.

With the above-described structure, when the rotation speed of the engine 1 reaches the switching set value set in advance by the tachometer 40 according to the working conditions, the opening / closing valve 41 is operated via the switch device 42 to activate the actuator 7 The pressure oil flowing through the high-pressure side pipe line 33 supplied to the valve can be led to the low-pressure side pipe line 34 to make the pressure applied to the actuator 7 constant. In this embodiment, since the switching set value is set by electrical means, it is extremely easy to select or change the set value as compared with the previous two examples, and an instruction to start the control for performing this type of control is given. Since it can also be processed in the processing device 43, there is an effect that the configuration is simplified.

In the first embodiment, the pressure on the downstream side of the pressure reducing valve 16 according to the command of the target rotation speed of the engine 1 of the accelerator lever 17 is detected and used as a parameter, and in the second embodiment. That is, the throttle that correlates with the discharge amount from the fixed displacement pump 30 that is discharged by being regulated by the actual operating speed of the engine 1.
The differential pressure of about 32 is used as a parameter, and in the third embodiment, the actual operating speed of the engine 1 is directly detected and used as a parameter. At least one of the operating speeds is detected in the form of pressure, or the speed of rotation is converted into an electrical signal, and predetermined control is performed based on the detected value.

〔The invention's effect〕

As is clear from the above description, when the actuation means selects the actuation of the maximum pressure limiting means, the rotation speeds of the first and second hydraulic pumps are increased based on the increase of the engine speed by the operation of the accelerator lever. At this time, the discharge flow rate of the second hydraulic pump increases as the engine speed increases, but the first hydraulic pump limits the maximum output value that is originally output according to the value set by the maximum pressure limiting means. As it is designed to control the discharge flow rate,
The work can be performed by maximizing the discharge amount of the variable displacement hydraulic pump without adjusting the operation speed of the load, which can simplify the work and reduce the burden on the driver. Further, it is possible to increase the number of gear stages without using a mechanical gear changing means, and even if the gear stage is set to an extremely low speed, the driving torque does not increase, so it is not necessary to increase the strength of the drive shaft. There are remarkable effects such as no increase in cost.

[Brief description of drawings]

1 to 4 are for explaining an embodiment of the present invention. FIG. 1 is a circuit diagram of a hydraulic drive circuit according to the first embodiment, and FIG. 2 is a vehicle speed and a stroke of an accelerator lever. And FIG. 3 is a circuit diagram showing a main part of the hydraulic drive circuit according to the second embodiment, and FIG. 4 is a circuit showing a main part of the hydraulic drive circuit according to the third embodiment. FIGS. 5, 5 and 6 are for explaining a conventional example. FIG. 5 is a circuit diagram of a hydraulic drive circuit according to the conventional example, and FIG. 6 shows a relationship between a vehicle speed and a stroke of an accelerator lever. It is a characteristic diagram. 1 ... Engine, 2 ... Variable displacement hydraulic pump, 3 ... Hydraulic pump, 4 ... Hydraulic motor, 6 ... Swash plate, 7 ... Actuator, 8 ... Direction switching valve, 10,11 ... Main pipeline , 12
...... Transmission, 16 ...... Reducing valve, 17 …… Accelerator lever, 22
…… Sequence valve, 23 …… Pilot line, 24 …… Open / close valve, 25 …… Bypass line, 32 …… Throttle, 33,34 ……
Pipe line, 40 ... Tachometer, 41 ... Open / close valve, 42 ... Switch device, 43 ... Processing device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Sonoda, 650 Jinritsu-cho, Tsuchiura City, Ibaraki Prefecture, Tsuchiura Plant, Hitachi Construction Machinery Co., Ltd. (56) References 50-103082 (JP, U) JP 52-28948 (JP, B2)

Claims (1)

[Claims] 1. A first hydraulic pump for driving a wheel, comprising one engine, a variable discharge amount mechanism, and a second hydraulic pump connected to the engine for driving a working means.
A hydraulic motor connected to the first hydraulic pump, a hydraulic actuator that operates the discharge amount varying mechanism, an accelerator lever that is connected to the engine and that allows an operator to set a target rotation speed of the engine, and the hydraulic actuator. Connected between the hydraulic pressure source for supplying pressure oil to the hydraulic actuator and the hydraulic pressure source, and increases the pressure of the pressure fluid supplied to the actuator in accordance with an increase in the operation amount of the accelerator lever and transmits it. In a hydraulic drive circuit that includes a hydraulic oil transmission unit that operates and a low pressure circuit that is connected to the actuator and the hydraulic oil transmission unit and that allows the hydraulic oil supplied from the hydraulic pressure source to pass therethrough. The working pressure oil from the working oil transmission means is used at a pressure value lower than the maximum pressure value that can be output to the actuator. A maximum pressure limiting means for limiting the maximum value of the supply pressure to the hydraulic actuator by bypassing the pressure circuit, and an operating means operated by the operator to selectively operate the maximum pressure limiting means are provided. When the actuation means selects the actuation of the maximum pressure limiting means, when the rotation speeds of the first and second hydraulic pumps are increased based on the increase of the engine rotation speed by the operation of the accelerator lever, the discharge of the second hydraulic pump is performed. The flow rate increases as the engine speed increases, but the first hydraulic pump is controlled to have a discharge flow rate that is limited from the maximum value that is originally output according to the value set by the maximum pressure limiting means. A hydraulic drive circuit characterized in that